Powder metallurgy is a technique for manufacturing sintered parts, such as machine parts, by pressing a mixed power that includes an iron-based powder to obtain a green compact and then sintering the green compact. Recent advances in powder metallurgy techniques have allowed sintered parts with complex shapes to be manufactured to a near net shape with high dimensional accuracy. Powder metallurgy techniques are now used to manufacture products in a variety of fields.
The sintered parts may, however, need post processing (such as cutting work) when extremely strict dimensional accuracy is required or when a horizontal hole, undercut, or other such highly complicated shape is required.
However, sintered parts are too strong for post processing and have a high ratio of holes, increasing the cutting resistance and frictional heat. The surface temperature of the cutting tool thus tends to rise, causing the cutting tool to wear easily and have a shorter life. This leads to the problem of an increase in the cutting work cost and an increase in the manufacturing cost of sintered parts.
To address this issue, green machining, whereby the green compact is subjected to cutting work before being sintered, has attracted attention. The green compact before sintering is typically brittle, however, and often has insufficient machinability. In other words, the green compact before sintering cannot withstand the stress that occurs during mounting on a jig for green machining or during cutting work and thus damages easily. Attempts have therefore been made to increase the strength of a green compact so as to withstand green machining.
For example, in a metal powder composition containing an iron-based powder and a lubricant powder, JP 3803371 B2 (PTL 1) proposes using an amide type oligomer with a weight average molecular weight MW of 2,000 to 20,000 and a melting point peak of 120° C. to 200° C. as the lubricant powder.